The effect of the morphology of coronal holes on the propagational evolution of high-speed solar wind streams in the inner heliosphere
- 1Leibniz Institute for Astrophysics Potsdam, Solar Physics, Germany (stefan.hofmeister@web.de)
- 2Department of Physics, University of Helsinki, Finland
- 3CAS Key Laboratory of Geospace Environment, University of Science and Technology of China, Hefei, PR China
- 4Institute of Experimental and Applied Physics, University of Kiel, Germany
- 5Solar-Terrestrial Centre of Excellence – SIDC, Royal Observatory of Belgium, Brussels, Belgium
- 6Centre for mathematical Plasma Astrophysics (CmPA), Department of Mathematics, KU Leuven, Belgium
- 7Institute of Physics, University of Graz, Graz, Austria
- 8National Space Institute, Technical University of Denmark, Copenhagen, Denmark
- 9Hvar Observatory, Faculty of Geodesy, University of Zagreb, Croatia
Since the 1970s it has been empirically known that the area of solar coronal holes a ects the properties of high-speed solar wind
streams (HSSs) at Earth. We derive a simple analytical model for the propagation of HSSs from the Sun to Earth and thereby show
how the area of coronal holes and the size of their boundary regions a ect the HSS velocity, temperature, and density near Earth.
We assume that velocity, temperature, and density profiles form across the HSS cross section close to the Sun and that these spatial
profiles translate into corresponding temporal profiles in a given radial direction due to the solar rotation. These temporal distributions
drive the stream interface to the preceding slow solar wind plasma and disperse with distance from the Sun. The HSS properties at
1AU are then given by all HSS plasma parcels launched from the Sun that did not run into the stream interface at Earth distance.
We show that the velocity plateau region of HSSs as seen at 1AU, if apparent, originates from the center region of the HSS close
to the Sun, whereas the velocity tail at 1AU originates from the trailing boundary region. Small HSSs can be described to entirely
consist of boundary region plasma, which intrinsically results in smaller peak velocities. The peak velocity of HSSs at Earth further
depends on the longitudinal width of the HSS close to the Sun. The shorter the longitudinal width of an HSS close to the Sun, the
more of its “fastest” HSS plasma parcels from the HSS core and trailing boundary region have impinged upon the stream interface
with the preceding slow solar wind, and the smaller is the peak velocity of the HSS at Earth. As the longitudinal width is statistically
correlated to the area of coronal holes, this also explains the well-known empirical relationship between coronal hole areas and HSS
peak velocities. Further, the temperature and density of HSS plasma parcels at Earth depend on their radial expansion from the Sun
to Earth. The radial expansion is determined by the velocity gradient across the HSS boundary region close to the Sun and gives the
velocity-temperature and density-temperature relationships at Earth their specific shape. When considering a large number of HSSs,
the assumed correlation between the HSS velocities and temperatures close to the Sun degrades only slightly up to 1AU, but the
correlation between the velocities and densities is strongly disrupted up to 1AU due to the radial expansion. Finally, we show how
the number of particles of the piled-up slow solar wind in the stream interaction region depends on the velocities and densities of the
HSS and preceding slow solar wind plasma.
How to cite: Hofmeister, S., Asvestari, E., Guo, J., Heidrich-Meisner, V., Heinemann, S., Magdalenic, J., Poedts, S., Samara, E., Temmer, M., Vennerstrom, S., Veronig, A., Vrsnak, B., and Wimmer-Schweingruber, R.: The effect of the morphology of coronal holes on the propagational evolution of high-speed solar wind streams in the inner heliosphere, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-14753, https://doi.org/10.5194/egusphere-egu23-14753, 2023.
